1. Field of the Invention
The present invention relates to a data communication system, a printing system and a data communication apparatus, and in particular to a system in which data are exchanged among apparatuses.
2 Related Background Art
The most frequently employed peripheral devices for personal computers are hard disks and printers. For data communication, these peripheral devices are connected to personal computers by a digital interface (hereinafter referred to as a digital I/F) such as a SCSI IF, which is a typical, general-purpose interface for small computers.
Digital cameras and digital video cameras are also types of peripheral devices used as input means for personal computers (hereinafter referred to as PCs). As the technique has been developed, static pictures and animated pictures acquired by a digital camera or a video camera are fetched to a PC for storage on a hard disk, or are edited by using a PC and are printed on a color printer, and users for the digital cameras are increased.
The image data are transmitted, via the above described SCSI IF, from a PC to a printer or to a hard disk. In order to transmit such a large quantity of image data, a general-purpose digital I/F having a high data transfer rate is required.
As is described above, conventionally, peripheral devices are connected to a host PC, and image data obtained by a camera are printed by routing them through the PC.
FIG. 3 is a block diagram illustrating an example general interface for a PC. A digital camera 31 is connected to a personal computer (PC) 32 by using a digital I/F, and a printer 33 is connected via a SCSI IF.
In FIG. 3, the digital camera 31 comprises: a memory 34, used as a storage unit; an image data decoder 35; an image processing unit 36; a D/A converter 37; a EVF 38 as a display unit; and a digital I/O unit 39.
The PC 32 comprises a digital I/O unit 40, for interfacing the PC 32 with the digital camera 31; an operating unit 41, such as a keyboard or a mouse; an image data decoder 42; a display 43; a hard disk 44; a memory 45, such as a RAM; an MPU 46, used as a processing unit; a PCI bus 47; and a SCSI interface (board) 48, used as a digital I/F. The PC 32 is connected to the printer 33 via the SCSI I/F 48.
The printer 33 comprises: a SCSI interface (I/F) 49, connected to the PC 32 by a SCSI cable; a memory 50; a printer head 51; a printer controller 52; and a driver 53.
With this arrangement, a video signal (image data) obtained by the digital camera 31 is transmitted to the PC 32. The image data are edited by the PC 32 and the edited data are output to the printer 33. When the image data stored in the memory 34 of the digital camera 31 are read, they are decoded by the decoder 35, and the resultant data are processed by the image processing unit 36 for display on the EVF 38. The data are then routed through the D/A converter 37 and displayed on the EVF 38. The image data from the memory 34 are transmitted via a cable from the digital I/O unit 39 to the digital I/O unit 40 in the PC 32.
In the PC 32, the image data received from the digital I/O unit 40 are stored on the hard disk 44 via the PCI bus 47, which is an inter-transmission bus, or are decoded by the decoder 42 and the decoded data are stored in the memory 45 or presented on the display 43. To print the image data, the data are transmitted from the SCSI interface board 48 of the PC 32 along the SCSI cable to the printer 33. The printer 33 receives the image data at the SCSI interface 49, and stores them in the memory 50. Thereafter, the print controller 52 reads the print image data from the memory 50 and outputs them to the driver 53, and images based on the print image data are printed by the printer head 51.
As is described above, conventionally the peripheral devices are connected to the host PC 32, and data are exchanged between the peripheral devices via the PC 32.
However, among the SCSI IF used in the prior art, some have low data transfer rates or require thick cables for parallel communication, and the types and numbers of peripheral devices that can be connected to these IFs, and the connection systems, are limited. In addition, the inconvenience in many aspects is pointed out.
Many common home PCs have connectors on the rear face for connecting the attachment of SCSI and other cables, and the shape and size of the SCSI connector are such that its insertion and removal are not easy. A mobile or portable device, such as a digital camera or a video camera, which is not normally installed, must also be connected to the connector on the rear of the PC, and this is very difficult.
Usually, many peripheral devices are connected to a personal computer. As the types of peripheral devices have increased, and as I/Fs have been developed, in addition to the PC peripheral devices, many digital apparatuses can be connected across a communication network. While for data communication this is very convenient, a very large amount of data are also frequently communicated between specific devices, which will cause a heavy traffic in the network and adversely effect the communication between other devices in the network. For example, if a user desires sequential or rapid image printing, communication between devices that a user is not aware of may affect the whole network of a host PC during the data communication between the PC and a printer, so that image printing can not be normally performed, or is delayed. As is described above, there is also a load imposed on a PC due to the heavy traffic on a network, or a defect of print data communication due to the operating state of the PC.